Earth-moving or material-handling machines, such as excavators, tractors, harvesters, forwarders or cranes, may be used in a large variety of applications such as for digging trenches, holes and foundations, demolishing buildings and other structures, landscaping, construction, mining and river dredging, harvesting and forwarding logs, lifting and placing objects etc. The versatility of such machines increases considerably when their tools can be rapidly changed and/or positioned by tilting and/or turning relative to their articulated arm. A mechanically or hydraulically operated device enabling one or several of these functions significantly enhances the productivity of the machine. The device for coupling and/or positioning (tilt and/or turn) has to be made from a material that possesses both strength, toughness and wear resistance in order to be able to withstand the significant mechanical stresses that it may be subjected to during the use of the machine with various tools.
Most of such devices are manufactured by welding several machined plates of steel together, followed by final machining. To reduce distortions caused by welding stresses, a stress relieving heat treatment is often necessary before final machining. Further, the device surfaces that come into contact with part of a tool or some other component, such as a gear or a bearing, when in use, may require local hardening or treatment to improve their wear resistance. Alternatively, some of the tribological requirements of the contact surfaces are satisfied by using softer and chemically different (i.e. compared to steel and iron) materials, such as bronzes, to avoid adhesive wear and seizure. However, this has several drawbacks: they cannot withstand high contact forces without continuing plastic deformation after initial running in and thus have to be replaced periodically. They may also be problematic to join to iron-based load-bearing structures.
It is often not economically feasible to manufacture steel devices by casting, especially if the devices are required to have a complex shape. This is because large risers (providing additional melt to castings as they solidify during cooling) are necessary to produce devices that are free of internal shrinkage voids, due to the large volume shrinkage in steel as it solidifies. Such large and numerous risers add cost and complexity to the device manufacturing process. To obtain sufficient mechanical properties in cast steel devices, hardening followed by tempering is necessary before final machining. A stress relieving heat treatment may also be necessary before final machining. Further, the device surfaces in contact with the tool may require local hardening to improve wear resistance.
The solidification shrinkage in ductile iron castings is less than half of that of steel castings, but in case of the device coupling interfaces in contact with the tool, ductile iron does often not have sufficient mechanical properties in the as-cast condition.